Security was stepped up outside Sri Lanka's top court on Friday ahead of an expected ruling on whether the president broke the law by sacking parliament last month, a decision that could potentially lead to impeachment proceedings.
Four days later, the Supreme Court issued an interim ruling suspending Sirisena's decree and restoring parliament, which almost immediately passed a no-confidence motion against Rajapakse.
The court's seven-judge bench was likely to deliver a final ruling on the constitutionality of Sirisena's move on Friday.
"If the morning session is brief, we can expect a decision later today," a court official said.
Sacked premier and their allies, who command a majority in the 225-member assembly, have suggested that they could begin impeachment proceedings again Sirisena depending on the ruling.
Wickremesinghe's party loyalists believe that the court decision will go in their favour, a view held by many independent lawyers.
Problems for Sirisena were compounded on Monday when the Court of Appeal suspended the entire cabinet and asked Rajapakse to explain on what authority he was holding office.
With parliamentary proceedings degenerating into brawls, the United States, the European Union and other powers have raised concerns over the crisis in the strategically important island nation of 21 million people.
Only China has recognised the appointment of Rajapakse, who during his decade as president until 2015 relied heavily on Beijing for diplomatic and financial support.
As president from 2005 until 2015, he ended Sri Lanka's four-decade civil war in 2009 by crushing the rebel Tamil Tigers.
But 40,000 ethnic Tamils were allegedly massacred in the process. Rajapakse and his family are also alleged to have profited from his time in power through corrupt deals.
During an earlier stint as prime minister from 2001 until 2004, Wickremesinghe is credited with pulling Sri Lanka out of its first ever recession, in part with reforms that have endeared him to the West.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)